Experimental evidence will be sought to link cataract production with the effects of chemical agents and with the effect of combined treatment with long-wave ultra-violet light and photosensitizers. Pre-cataractous changes will be monitored by measuring changes in lens permeability to such tracers as alpha-aminoisobutyric acid, galactose, fructose, lactic acid, leucine, mannitol, 3-0-methylglucose and thiourea.